Add More Data Sources to SearchAgent

[YanCotta]

Description:

The SearchAgent currently relies on a mock web search. To make the research workflow more powerful, we should add support for more data sources, such as APIs for academic papers (e.g., arXiv, Semantic Scholar) or news articles.

Acceptance Criteria:

[ ] The _perform_web_search method in src/agents/async_search_agent.py should be updated to query at least one new data source API.

[ ] The results from different data sources should be combined and normalized before being sent to the orchestrator.

[ ] The new data sources should be configurable via environment variables.

[ ] The README.md should be updated to document the new data sources and how to configure them.

Files to check:

src/agents/async_search_agent.py